Gaming machines, such as slot machines, video poker machines and the like, have been a cornerstone of the gaming industry for several years. Generally, the popularity of such machines with players is dependent on the likelihood (or perceived likelihood) of winning money at the machine and the intrinsic entertainment value of the machine relative to other available gaming options. Where the available gaming options include a number of competing machines and the expectation of winning each machine is roughly the same (or believed to be the same), players are most likely to be attracted to the most entertaining and exciting of the machines. Shrewd operators consequently strive to employ the most entertaining and exciting machines available because such machines attract frequent play and hence increase profitability to the operator. Accordingly, in the competitive gaming machine industry, there is a continuing need for gaming machine manufacturers to produce new types of games, or enhancements to existing games, which will attract frequent play by enhancing the entertainment value and excitement associated with the game.
One concept which has been successfully employed to enhance the entertainment value of a game is the concept of a "secondary" or "bonus" game which may be played in conjunction with a "basic" game. The bonus game may comprise any type of game, either similar to or completely different from the base game, which is entered upon the occurrence of a selected event or outcome of the base game. The bonus game concept is the subject of U.S. parent patent application Ser. Nos. 08/835,840 ("the '840 application") filed Apr. 23, 1997 and 09/140,947 ("the '947 application") filed Aug. 27, 1998, both of which are assigned to the assignee of the present application and incorporated herein by reference in their entireties. The '840 and '947 applications disclose an embodiment wherein the base game is a reel-type slot machine and the bonus game is a simulated reel-type slot machine implemented on a video-type display. The bonus game is entered upon the appearance of a special symbol combination of start-bonus symbols on the reels of the slot machine in the base game. In the bonus game, the probability of winning combinations appearing on the reels, or the "hit rate," is much greater than that of the base game. The player is permitted to keep playing and accumulate winnings from the bonus game until a losing trial occurs. Such a bonus game produces a significantly higher level of player excitement than the base game because it provides a greater expectation of winning than the base game and is accompanied with more attractive or unusual video displays and/or audio.
Because the bonus game concept offers tremendous advantages in player appeal and excitement relative to other known games, and because such games are attractive to both players and operators, there is a continuing need to develop new features for bonus games to satisfy the demands of players and operators. Preferably, such new bonus game features will maintain, or even further enhance, the level of player excitement offered by bonus games heretofore known in the art. The present invention is directed to satisfying these needs.